Why we developed the ability to drink milk

One of the most fascinating areas of modern science is the emergent power of genetic analysis to tease out bits of history, with prominent examples such as the lineage of Sally Hemings and the promiscuity of Genghis Khan.

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Thank your sun-deprived ancestors.

But for me the most powerful results come from using genetics to study ancient human history. Like understanding the question why we drink milk.

Humans require the lactase enzyme to digest milk, and in most humans the activity of this enzyme falls off as toddlers grow into adolescents and then adults. But not for those of European descent or certain nomadic populations. Why?

According to a new paper in PLoS One, there’s not a single explanation.

It’s been known that different populations in Europe and Africa independently evolved the capacity to drink milk about 7,000 years ago, around the time people were beginning to domesticate cattle. And now, the new paper confirms, it turns out that each adult population developed the ability to digest milk for different reasons.

Europeans developed the ability to drink milk because the calcium made their bones stronger in climates where there wasn’t as much sunlight, and therefore vitamin D. The further south you go in Europe, the lower the percentage of people that can digest lactose.

And the Africans? They appear to have developed the ability to digest lactose in adulthood because it was simply a good course of protein and calories.

If you’re interested in a slightly more technical take on the new paper and the issue in general, Jeremy Yoder has a nice write-up of the paper.